The invention relates to a device for inspecting eggs for the presence of blood. The device comprises a light source in order to pass light of a first wavelength, which is not selectively absorbed by blood, and light of a second wavelength, which is selectively absorbed by blood, through an egg to be inspected. The device further comprises detection means for converting the light transmission through the egg to be inspected for each of the two wavelengths into corresponding signals, each of the said signals being representative of the light transmission at the relevant wavelength. Furthermore the device comprises signal-processing means which are designed to determine the ratio between the light transmission associated with the first wavelength and the light transmission associated with the second wavelength based on the signals emanating from the detection means and to emit a decision signal which is representative of the decision whether or not an egg contains blood on the basis of this ratio.
A device of this type is known from NL 7504011. The light transmission is the light energy which is transmitted through the egg at the two wavelengths. With eggs that do not contain blood, the ratio of the measurements of the transmitted light energy at the two different wavelengths is virtually fixed. With eggs that do contain blood, the light of the second wavelength is absorbed more than the light of the first wavelength as a result of the presence of blood in the egg, which disturbs the ratio between the transmitted light energy at the two wavelengths. This disturbance is converted by the device into a decision signal which indicates that the egg contains blood and therefore has to be rejected. With the known device, different light sources are used for the light of the first wavelength and of the second wavelength. In particular, for the first wavelength, a halogen lamp with an interference filter is used in the known device. For the second wavelength, a mercury spectral lamp with an interference filter is used. The known device further comprises what is known as a rotating butterfly which covers either both or one of the two light sources alternatively, as a result of which alternately a light beam from the one and from the other light source hits the egg. When the butterfly covers both lamps, no light falls on the detection means and what is known as a zero measurement can be carried out in order to compensate for the offset of the detection means.